This invention relates to a method for explosive cladding to be utilized for the production of clad metal composites intended for use in, for example, chemical reaction vessels and electronic sensors, and to explosive clad metal composites comprising two or more layers of the same or different metal.
Explosive cladding a layer of one metal to another layer of the same or different metal by using the force of explosion of an explosive such as dynamite or powdered high explosive has been recently well known and used all over the world.
In explosive cladding with dynamite, since the dynamite has a low-speed detonation region and a high-speed detonation region, the detonation velocity changes while the explosion-cladding is carried out and, consequently, uneven cladding takes place fairly frequently. The explosive cladding with powdered high explosive has the disadvantage that this explosive is not economical because preparation of the explosive entails time and labor. Generally the detonation velocity of a powdered high explosive depends on the thickness of the layer of the powdered explosive. Thus, from the standpoint of a performance, the explosive cladding with a powdered high explosive has the disadvantage that uniform setting of the explosive is difficult and defective cladding of metal is liable to occur, and the operation itself consequently turns out to be very expensive.
The present inventors continued a study in search of a method which effects an explosive cladding without causing such defects as uneven cladding and which is economic from the operational point of view. As a result, they have found that a method of explosive cladding, in which a water-in-oil type (hereinafter referred to as "w/o" type) emulsion explosive is used, is capable of effecting the explosive cladding without causing any defective cladding and economical as compared with the conventional methods. More precisely, the present inventors have found that the w/o type emulsion explosive exhibits an exceptionally stable detonation velocity and further that the detonation velocity of the w/o type emulsion explosive can be easily regulated in a range from 5,000 m/sec to 2,000 m/sec by suitably selecting the amount of minute hollow spheres contained in the w/o type emulsion explosive thereby varying the specific gravity thereof. The present invention has been on the basis of these findings. Table 1 shows typical experimental details on the specific gravity and the detonation velocity of the w/o type emulsion explosives measured by the present inventors.
TABLE 1 ______________________________________ Detonation velocity No. Specific gravity (m/sec) ______________________________________ 1 1.25 4,460 2 1.20 5,020 3 1.10 4,900 4 1.00 4,520 5 0.90 4,080 6 0.80 3,680 7 0.70 3,220 8 0.60 2,800 9 0.50 2,320 10 0.40 2,050 ______________________________________
Composition of explosive: PA0 Detonation velocity: This property was determined by the ion gap method in a paper cartridge of 30 mm in diameter. PA0 The results given in this table were obtained by using the w/o type emulsion explosive identified as No. 4 in Table 1. PA0 The w/o type emulsion explosive was formed into a layer having a fixed width of 50 mm and a varying thickness and the detonation velocity was measured by the ion gap method. PA0 The measurement of the detonation velocity was carried out in a paper cartridge of 30 mm in diameter. PA0 The number marked by "*1" denotes the w/o type emulsion explosive identified by the same number in Table 1. PA0 The length marked by "*2" denotes the distance from the bottom of the detonator. The detonation velocity at 1 cm represents the average detonation velocity measured over a distance of 1 cm from the bottom of the detonator to the point of 1 cm, the detonation velocity at 2 cm represents the average detonation velocity measured over a distance of 1 cm from the point of 1 cm to that of 2 cm, and so on.
Emulsion--71% of ammonium nitrate, 10% of sodium nitrate, 13% of water, 4% of carbonaceous fuel, and 2% of emulsifier (by weight) PA1 Minute hollow spheres--Glass bubbles, produced by 3M Corp. and marketed under trademark of "C15" (The amount of the glass bubbles added to the emulsion was varied according to specific gravity desired.)
It has been found by the present inventors that, as noted in Table 1, the detonation velocity of the w/o type emulsion explosive can be easily controlled by specific gravity thereof and that the w/o type emulsion explosive, therefore, is proved to be suitable for a method of explosive cladding which requires, a variable detonation velocity according to the kinds of metals to be clad.
TABLE 2 ______________________________________ Thickness Detonation velocity (mm) (m/sec) ______________________________________ 15 4,550 20 4,530 30 4,540 40 4,610 ______________________________________
The inventors have further found that, as clearly noted in Table 2, the detonation velocity of the w/o type emulsion explosive is hardly variable with the thickness of the layer (cartridge diameter) thereof. The characteristic that the detonation velocity is not easely varied by the thickness results in the advantage that no defective cladding is caused even in the presence of a moderate unevenness in the thickness of the layer of the explosive and as a result the time and labor to be spent in setting the explosive is greatly saved. This characteristic further leads to the fact that a change in thickness of the layer of cladding metal (flyer) can be coped with by merely changing the thickness of the layer of the w/o type emulsion explosive. The method of explosive cladding according to the present invention is, therefore, far excellent compared with the conventional method of explosive cladding in terms of ease of the work and ease of the design of explosive cladding.
It has been further found by the present inventors that, as shown in Table 3, the start-up of the detonation velocity of the w/o type emulsion explosive rises quickly.
TABLE 3 ______________________________________ Explosive Dynamite 2*.sup.1 5*.sup.1 8*.sup.1 "Shinkiri" ______________________________________ Detonation 1*.sup.2 cm 5010 3950 3000 980 velocity 2*.sup.2 cm 4950 4130 2860 1300 (m/sec) 3.sup.*2 cm 5030 4050 2820 1410 4*.sup.2 cm 5130 4010 2950 4320 5*.sup.2 cm 4920 4120 3010 4180 6*.sup.2 cm 5010 4070 2880 4520 ______________________________________
This quick rise of the detonation velocity make a leading portion unnecessary in the actual operation of the explosive cladding. It also results in an effect of decreasing the amount of the explosive to be used. Though this effect is not conspicuous where the metals to be clad are large, it is relatively conspicuous where the metals to be clad are small. For example, when a flyer metal of 10 cm in length is to be clad with parent plate, the w/o type emulsion explosive has absolutely no need for any leading portion but the dynamite "Shinkiri" requires use of a leading portion of 4 cm in length. This fact clearly shows that the dynamite must be used in an appreciably larger amount than the w/o type emulsion explosive. When plural explosive claddings of such a small size are to be simultaneously carried out, the effect of abating noise and vibration with less the amount of the w/o type emulsion explosive in use is quite conspicuous.
Further, it has been found by the present inventors that the w/o type emulsion explosive does not cause a pain such as headache to a person handling it due to inhalation thereof because it contains no nitro compound such as nitroglycerin and nitroglycol. It has been further found that, when this w/o type emulsion explosive is put to use in the explosive cladding, it can be easily molded, as it is similarly to the dynamite, even in such special shapes which cannot be obtained if the powdered explosive is used and, as a result, the w/o type emulsion explosive enjoys notably improved workability. This effect in the improved workability is effective, expecially in small size explosive cladding.
It has been also found by the present inventors that the w/o type emulsion explosive has an oil phase as the external phase and, therefore, is superior to the powdered explosive in waterproofness and moistureproofness, that is, even when the w/o type emulsion explosive is left standing long in a state open to air, it has no possibility of absorbing moisture and suffering from degradation of quality unlike the powdered explosive and found that the w/o type emulsion explosive can be used with no problem when the explosive cladding is carried out under highly humid conditions such as the outdoors in the rain.
The present inventors have further found that when the w/o type emulsion explosive used in the explosive cladding has a specific gravity preferably below 0.9, more preferably below 0.8, most preferably in the range of 0.4 to 0.7 and a detonation velocity of not more than 80% of the sonic velocity (Vm) in the metal to be clad (calculated by the following formula), the effect of the explosive cladding is uniform and highly desirable. ##EQU1## wherein Vm stands for the sonic velocity in the metal, K for the bulk modulus, G for the share modulus, and .rho. for the density.
Heretofore, the explosive cladding of such special metals as copper and titanium by the use of dynamite or powdered explosive has necessitated adoption of an extremely time-consuming and expensive method in which the specific gravity of the explosive and the thickness of the layer thereof must be controlled to a given value with high accuracy for the purpose of ensuring uniformity of the cladding. By the method of the present invention, such special metals as mentioned above can be easily clad with high uniformity owing to the use of the w/o type emulsion explosive which has a specific gravity preferably below 0.9, more preferably below 0.8, most preferably in the range of 0.4 to 0.7 and a detonation velocity of not more than 80% of the sonic velocity in the metal.
It has been also found by the inventors that, when the w/o type emulsion explosive having a specific gravity in the range of 0.4 to 0.7 and a detonation velocity of not more than 80% of the sonic velocity in the metal is used in the explosive cladding, flyer metals having a very small thickness of not more than 2 mm or of an extremely thin thickness of not more than 0.7 mm can be easily and uniformly clad by using the explosive in a very small amount.
The detonation velocity of the w/o type emulsion explosive is preferred, as described above, to be not more than 80% of the sonic velocity in the metal. However, when the metal is one such as copper, brass, iron, aluminum, titanium, stainless steel, nickel, Hastelloy, etc., the w/o type emulsion explosive to be used in the explosive cladding is preferred to possess a detonation velocity in the range of 2,000 to 3500 m/sec for the purpose of ensuring high uniformity of the cladding.
In contrast to the conventional powdered explosive or dynamite which is so flammable and so sensitive to shocks as to render the handling thereof dangerous, the w/o type emulsion explosive used in the present invention has the advantage that the w/o type emulsion explosive is very safe to handle because it is not highly flammable and is insensitive to shocks.
The explosive clad metal composite which is obtained by the method of explosive cladding according to the present invention shows a higher shear strength than the clad metal composite obtained by the conventional method of explosive cladding as shown in Example 3 presented subsequently.